Reinvestigation of the microwave spectrum of 2-methylmalonaldehyde

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Title:	Reinvestigation of the microwave spectrum of 2-methylmalonaldehyde
Authors:	Vadim V. Ilyushina Eugene A. Alekseev Yung-Ching Chou Yen-Chu Hsu Jon T. Hougen Frank J. Lovas Laura B. Picraux 周永慶
Contributors:	臺北市立教育大學自然科學系
Date:	2008
Issue Date:	2009-07-31 15:41:33 (UTC+8)
Abstract:	The molecule 2-methylmalonaldehyde (2-MMA) exists in the gas phase as a six-membered hydrogen-bonded ring [HOCHC(CH3)CHO] and exhibits two large-amplitude motions, an intramolecular hydrogen transfer and a methyl torsion. The former motion is interesting because transfer of the hydrogen atom from the hydroxyl to the carbonyl group induces a tautomerization in the ring, which then triggers a 60° internal rotation of the methyl group attached to the ring. We present a new experimental study of the microwave spectra of the 2-MMA-d0 [HOCHC(CH3)CHO] and 2-MMA-d1 [DOCHC(CH3)CHO] isotopologs of the molecule. The new measurements were carried out by Fourier-transform microwave (FTMW) spectroscopy in the 8–24 GHz frequency range and by conventional absorption spectroscopy in the 49–149 GHz range. In the present work, we use a tunneling-rotational Hamiltonian based on a group-theoretical formalism to carry out global fits of 2578 2-MMA-d0 transitions and 2552 2-MMA-d1 transitions to measurement uncertainty, obtaining a root-mean-square deviation of 0.015 MHz for both isotopologs. This represents a significant improvement in fitting accuracy over past attempts. Some problems associated with calculating barrier heights from the observed tunneling splittings and assumed tunneling paths are also considered.
Relation:	Journal of Molecular Spectroscopy, V251(1-2), P.56-63
Appears in Collections:	[Department of Applied Physics and Chemistry] Periodical Articles

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